Two Fused Five-Membered Rings

Strategies for Organic Drug Synthesis and Design, Second Edition. By Daniel Lednicer Copyright 2009 John Wiley Sons, Inc. 

A related scheme starts with the conversion of the exocyclic amino group in 2-methylaminoimidazohne to a good leaving group by conversion to its nitramine derivative (5-2). Reaction of that intermediate with phenylethanolamine (5-1) leads to the displacement of the nitramine by the primary amine on the reagent and the formation of the substitution product (5-3). This is then cyclized with concentrated sulfuric acid to give an imidazoimidazole, probably via the benzylic carbocation. There is thus obtained imafen (5-4) [5], a compound described as an antidepressant. 

---

B. Compounds with Two Fused Five-Membered Rings. 279... 

The 1,3-cyclopentanediyl (62) motif has been further expanded into a bicycUc module containing two fused five-membered rings. The 2,2-disubstituted... 

For his synthesis of the anti-tumour compound diketo-coriolin, Danishefsky needed (9) with its two fused five-membered rings, Enone disconnection suggests two possible precursors. 

The number of methods available for the synthesis of bicyclic systems containing two fused five-membered rings with one bridgehead nitrogen can be summarized in a few general reactions dehydrative ring closure, oxidative Schiff base cyclization, and base-induced closure (Scheme 3). One-pot reactions involving precursor synthesis followed by cyclization are also known. 

Two Fused Five-membered Rings Each Containing One Heteroatom Volume 4 References... 

---